1. Field of the Invention
The present invention relates to the field of vacuum pick tools which are used to pick components from carrier tapes or other mechanisms for delivering such components to the site of a pick and place machine, wherein the pick and place machine removes the component from its carrier mechanism and moves it to a location on electronic circuit boards.
2. Description of the Prior Art
Vacuum pick tools of conventional design are used for components with the nominal X-Y-Z dimensions as small as 0.5×0.5×0.25 min and a flat upper surface, Such vacuum tools have a conical or pyramid exterior shape and a single through hole fitted to a tubular extension connected to the placement machine vacuum pick tool positioning mechanism to access and pick a repetitive sequence of components on or in continuous carrier tapes when repeatably indexed by a tape feeder to a designated pick point.
Assembly of electronic circuits comprising very small micro-sized surface mount components is one area where precision handling of these units is required. Current methods include picking small components from continuous carrier tapes and then placing them on a circuit board using a vacuum nozzle to contact the top surface of the component. With larger devices there is generally sufficient smooth surface area to enable capture and retention of devices for reliable transport of component from the carrier tapes to a circuit board location without loss of positional accuracy for placement. As the size of components continues to shrink to keep pace with the demand for ever smaller finished assemblies, the surface area available for the vacuum pick nozzle engagement diminishes. With this reduced area and resulting compromise of retention forces, components are frequently not captured (known as “mispicks”). Repeated attempts to capture devices from carrier tape interrupt a continuous smooth production flow and thereby decrease machine throughputs. In other words, fewer completed circuit boards are produced in a given length of time per machine.
Additional problems result from improper pick of devices in a non-correctable orientation, attempted by machine vision. Such loss of orientation results in a rejection of circuit boards in their entirety with proportional loss in yields of finished products. In point of fact, the cost of rework is frequently greater than the loss experienced in classification as “scrap’.
In addition, the integrity of the entire circuit board is compromised as a result of ‘off line rework’ and becomes unacceptable procedure in many situations. Throughputs and yields are the overarching ratings for successful automated factories and must be continuously improved to remain competitive.
There are also mechanical grippers that are used on larger components that grip the components by their edges. They are generally constructed using a vacuum piston to close the gripper fingers on the component through a system of linkages and pivot points. While this can provide a positive grip on the component, it becomes very difficult to scale the mechanical components down to the level required for these smallest of sizes and control the gripping forces.